How Does Google identify selling or buying links, exchange links?

Matt Cutts says: " Sponsor Links or Partner Links in various sites will be identified as selling or buying links". He also gave some exmaples of penalized sites with that kind of links. While, I know some good websites which live with buying links and avoding being penalized. Here is an official link about shceme links from Google webmaster http://support.google.com/webmasters/bin/answer.py?hl=en&answer=66356". This page mentions about Text advertisements that pass PR, Links distributed in site footers. How do you think Google's judgement on selling or buying links, exchanges? Have you experience any penality after panda and penguin?

Full article: http://forums.seochat.com/google-page-rank-47/how-does-go...

Tweets

@seo88888 » 27 Feb '13, 4pm
RT @ChariseStevens: How Does Google identify selling or buying links, exchange links? [link]
@seo88888 » 25 Feb '13, 10am
RT @YourMomBot: @whitegyr Your mom's selling or buying links, exchange links? [link]
@YourMomBot » 25 Feb '13, 10am
@whitegyr Your mom's selling or buying links, exchange links? [link]
@YourMomBot » 25 Feb '13, 10am
@chatpower_eu Your mom's selling or buying links, exchange links? [link]
@seo88888 » 25 Feb '13, 10am
RT @yousef_ghazawi: How Does Google identify selling or buying links, exchange links?: Matt Cutts says: " Sponsor Links or Partner... [link]
@yousef_ghazawi » 25 Feb '13, 10am
How Does Google identify selling or buying links, exchange links?: Matt Cutts says: " Sponsor Links or Partner... [link]
@seo88888 » 25 Feb '13, 10am
RT @whitegyr: How Does Google identify selling or buying links, exchange links? [link]
@whitegyr » 25 Feb '13, 10am
How Does Google identify selling or buying links, exchange links? [link]
@chatpower_eu » 25 Feb '13, 10am
How Does Google identify selling or buying links, exchange links? [link]